1. Field of the Invention
The present invention relates to wire stitching or stapling machines of the type which sever and form staples from a continuous wire and drive the staples into an associated workpiece. In particular, the invention relates to a rotatable wire holder for such a stitching machine.
2. Description of the Prior Art
The present invention is an improvement in a stitching machine head of the type which is sold by Interlake Packaging Corp. under the trade designation "CHAMPION STITCHER". One type of such a stitching machine head is disclosed, for example, in U.S. Pat. No. 4,410,123. The stitching machine head has a wire feed mechanism for feeding a predetermined length of wire from a continuous wire supply to a rotatable wire holder, where the length of wire is severed from the supply, and a staple forming and driving mechanism which forms the severed length of wire into a staple and drives it into an associated workpiece.
The wire feed mechanism and the staple forming and driving mechanism are coupled together so that they undergo a reciprocating movement in tandem, moving together in the same direction in response to an associated drive. Thus, the mechanism undergoes a cyclical reciprocating movement comprising a drive stroke and a return stroke. During each drive stroke the feed mechanism feeds a predetermined length of wire into a slot in the wire holder, while the staple forming and driving means forms and drives the length of wire which had been fed and cut during the preceding drive stroke. Both mechanisms then retract simultaneously, and at the end of each cycle there is left in the wire holder a severed length of wire ready to be formed and driven during the next drive stroke.
In the type of stitching machine head disclosed in the aforementioned U.S. Pat. No. 4,410,123, as the drive stroke begins, the cut length of wire which was fed in the previous cycle, is held in a horizontal orientation perpendicular to the direction of the drive stroke. During the drive stroke the wire is first formed over the wire holder by the staple forming and driving mechanism, which then cams the wire holder outwardly along its axis out of the path of the staple forming and driving mechanism, which picks up the formed staple and drives it into the associated workpiece. As the cut length of wire is being formed, a new length of wire is being fed parallel to the direction of the drive stroke into the holder slot behind a pivoting hook. As the wire holder is cammed out of the way by the staple forming and driving mechanism, a linkage rotates the wire holder on its axis through about 90.degree., in response to which the newly fed wire is guided by wire cam surfaces on the holder up out of the slot and onto substantially coplanar support surfaces on either side of the slot. As the drive stroke continues, the newly fed length of wire is severed from the supply, the severed length of wire being held against the support surfaces by the hook. During the retraction stroke the holder is pivoted back to its original orientation and, as the staple forming and driving mechanism clears it, moves axially back into its original position, returning the cut length of wire to a horizontal orientation for forming during the next cycle, the cut length of wire being held in place on the support surfaces by the hook during this rotation.
This type of rotatable wire holder has been subject to a number of disadvantages. It is prone to misfeeds, in that the leading end of the wire being fed into the holder may catch on the hook or on the edge of the slot accommodating the hook. The holder comprises movable parts, viz., the hook and its bias spring, which can fail and which necessitate costly and time consuming assembly. The slot for the hook is formed closely adjacent to and at an angle to the wire-receiving notch, resulting in a thin finger of material at one side of the slot which becomes brittle during heat treating of the holder and tends to break off in use.